Jump Bug Sync Issue

jacklick

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Donor 9 years: 2013, 2016-2021, 2023-2024
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1 step forward two steps back.

Game was working and still plays with constant scrolling. Rebuilt the 4600 monitor coincidentally? it won't sync now. I already tried adjusting Horz & Vert hold and Horz oscillator on monitor to no joy. The other tell tale is that the picture doesn't change at all when I completely remove the sync connector. I am not 100% ruling out monitor but previously there was no difference between board sync and tpg with the adjustments.

The monitor syncs fine to with just -H composite on TPG tester which is how the jump bug is wired.

I assume something has failed on the PCB but curious if there is an easy way to verify sync signal output while the pcb is still in the game.

Also, if anyone has a link to a manual that would be great.

Reference.
Another thread here by gamefixer which may be similar but is unresolved tmk
Jump Bug, Sega (G-04-JB)
https://segaretro.org/Galaxian-based_hardware
 
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videos are always good right? after watching it the Horz scroll reverses when cable is connected vs disconnected. Not sure if that means anything. This is the best I can possibly get it with adjustments.




 
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Made an adapter (just enough to coin up and start a game) so I could bring the board to bench. Sync is even worse on PVM. <<edit I can make it look like above by turning off ext sync on pvm..eg disconnecting sync

Haven't found a schematic yet but traced sync to r7 & r8 then to b5 pin 3 which is a 74LS08N

Coined up and started game and you can hear it play.

 
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Ok learning here... This almost seems too easy
74ls08 is a quad 2-input and gate. So pin 3 (composite sync line) is the output of pin 1 and 2 ( I assume vertical and horizontal sync)
I put my logic probe on pin 3 and it is stuck low. pin 1 has activity and pin 2 has activity at higher pace (whatever the term is).

Looks like I have a bad 74ls08 right?
 
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Pulled a 74ls08 off a donor board, socketed and replaced B5 and we are in business again.

not sure if the sounds are all 100% but it appears to be working.

 
Nice work. Great game that most folks have never played. I'm still trying to figure out why my star field will sometimes speed up, get choppy and then disappear if the machine has been on for more than 2-3 hours. It seems to happen randomly and not every time the machine is on. Gamefixer has verified that it is not a heat related issue, as he wrapped my PCB in a blanket while it was running to try and replicate the issue. Must be a bad chip.
 
Thanks Phet. I have been digging like crazy and the best documentation found is for Galaxian. Would be nice to have schematics for this board.

BTW. probably need a separate thread but it seems like there are two volume pots. VR2 might be volume and VR1 pitch or sound effects not sure. It sounds the best on bench with VR1 turned all the way clockwise and VR2 just turned up a bit. This results in the music being loud but the cymbal crash when you die being tolerable. If I adjust VR1 counter clockwise the cymbal sound gets loud and distorted.
 

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